Radiation Physics

matter

anything that occupies space and has mass

atom

small, invisible particle that is the fundamental unit of matter

central nucleus, orbital nucleus

what 2 parts does an atom consist of?

by composition of the nucleus and arrangement of orbiting electrons

how is an atom’s identity determined?

proton and neutrons

what is found in the atom’s nucleus?

nucleus

core of the atom

electrons

tiny, negatively charged; little mass; outer layer can be disrupted during xrays

binding energy/force

electrons are maintained in their orbits by electrostatic force between the positive nucleus and negative electrons

by the distance between the nucleus and the orbiting electron

how is binding energy determined?

molecules

2 or more atoms joined together by chemical bond

transfer of electrons, sharing of electrons on the outermost shell

how can molecules be formed?

ionization

production of ions or the process of converting an atom into ions

ion

an atom or molecule which has lost or gained electrons, makes it either positive or negative

radiation

emission and propagation of energy through space or a substance in the form of waves or particles; controlled

radioactivity

process by which certain unstable atoms or elements undergo spontaneous disintegration or decay in an effort to attain a more balance nuclear state; uncontrolled

particulate radiation, electromagnetic radiation

what are the 2 classifications of ionizing radiation?

particulate radiation

tiny particles of matter that possess pass and travel in straight lines at high speeds

elections, alpha particles, protons, neutrons

what are the 4 types of particulate radiation?

alpha particles

emitted from the nuclei of heavy metals; exist as two protons and neutrons, without electrons

protons

accelerated hydrogen nuclei; mass of 1 and charge of +1

neutrons

accelerated particles; mass of 1, no charge

electromagnetic radiation

propagation of wavelike energy (w/o mass) through space or matter; only high-energy radiations are capable of ionization; believed to to move through space as both a particle and a wave

particle concept

characterizes electromagnetic radiation in terms of discrete bundles of energy called photons or quanta

photons

bundles of energy with no mass or weight

wave concept

characterizes electromagnetic radiations as waves

velocity

the speed of the wave

wavelength

the distance between the crest of one wave and the crest of the next; determines energy and penetrating power of radiation

frequency

number of wavelengths that pass a certain point in a given length of time; shorter the distance between crests = shorter the wavelength = greater penetration

control panel, extension arm, tubehead, PID

what are the components of the dental xray machine?

contains on/off switch, indicator light, control devices, plugged into an electrical outlet

what does the control panel have?

extension arm

suspends the xray tubehead, houses the electrical wires that extend from the control panel to the tubehead, allows for movement and positioning of the tubehead

tubehead, metal housing, insulating oil, tubehead seal, xray tube, transformer, aluminum disks, lead collimator, position-indicating device

what are the components of the tubehead?

tubehead

where xrays are produced, inside all air has been pumped out to create a vacuum, immersed in an oil bath which provides electrical insulation and helps dissipate heat

xray tube

heart of the xray generating system, glass vacuum tube

leaded-glass housing, cathode, anode

what is included in x-ray tube?

leaded glass housing

prevents xrays from escaping in all directions, has window that permits xray beam to exit, encases the entire tube

cathode

negative electrode, consists of tungsten wire filament in a cup-shaped holder made of molybdenum, supplies the electrons necessary to generate xrays; hotter it is the more electrons produced

anode

positive electrode; consists of tungsten plate; converts electrons into xray photons

milliamperage (mA)

measurement of the number of electrons moving through a conductor; total quantity;

higher mA = darker radiograph

how to get darker radiograph?

kilovoltage peak (kVp)

measurement of electrical force that causes electrons to move from a negative pole to a positive one; controls speed of electrons (speed of electrons determines penetrating power); voltage increases, electrons travel faster

kVp increases = power increases = high quality

how to get better quality?

timer

regulates the length of time that the current will pass through the xray tube; controls film density (darker)

radiographic technique, type of xray film, tissues being radiographed, target-to-film distance

what is exposure time affected by?

low-voltage (filament) circuit, high-voltage circuit

what are the two electrical circuits used in the production of xrays?

mA

what is low-voltage circuit controlled by?

kVp

what is high-voltage circuit controlled by?

transformers

devices used to increase or decrease the voltage in an electrical circuit

step-down transformer, step-up transformer, autotransformer

what are the 3 transformers?

step-down transformer

decreases the voltage used by the low-voltage circuit, more wires are present in primary coil than secondary coil

step-up transformer

increases the voltage used by the high-voltage circuit, less wires present in the primary coil than the secondary coil

autotransformer

serves as a voltage compensator, corrects minor fluctuations in the current

general (braking) radiation, characteristic radiation

what are the 2 mechanisms of xray

general (braking) radiation

electron rarely hits the nucleus of the tungsten target but when it does all its kinetic energy is converted into a high energy xray proton

characteristic radiation

produced when a high-speed electron dislodges an inner-shell electron from a tungsten atom and causes ionization of that atom; produces loss of energy

primary radiation

penetrating xray beam that is produced at the target of the anode

secondary radiation

x-radiation created when the primary beam interacts with matter (head, skull, teeth, etc)

scatter radiation

result of an xray that has been deflected from its path by an interaction with matter; detrimental

absorption

total transfer of energy from photon to the atoms of matter

photoelectric effect

xray photon collides with a tightly-bound, inner-shell electron, gives up all its energy to eject the electron from its orbit

compton scatter

xray photon is deflected from its path during passage through matter; ionization takes place; photon collides with a loosely bound outer-shell electron and gives up part of its energy to eject the electron from its orbit; loses energy and continues in a different direction at a lower energy level

coherent scatter

xray photon that has its path altered with matter; lower energy photon interacts with an outer-shell electron; no change in the atom occurs